Several naturally-occurring alkaloids obtainable from Vinca rosea have been found active in the treatment of experimental malignancies in animals. Among these are leurosine (U.S. Pat. No. 3,370,057), vincaleukoblastine (vinblastine) to be referred to hereinafter as VLB (U.S. Pat. No. 3,097,137), leuroformine (Belgian Pat. No. 811,110); leurosidine (vinrosidine) and leurocristine (to be referred to hereafter as vincristine) (both in U.S. Pat. No. 3,205,220); deoxy VLB "A" and "B", Tetrahedron Letters, 783 (1958); 4-desacetoxyvinblastine (U.S. Pat. No. 3,954,773); 4-desacetoxy-3'-hydroxyvinblastine (U.S. Pat. No. 3,944,554); leurocolombine (U.S. Pat. No. 3,890,325) and vincadioline (U.S. Pat. No. 3,887,565). Two of these alkaloids, VLB and vincristine, are now marketed as drugs for the treatment of malignancies, particularly the leukemias and related diseases in humans. The two marketed alkaloids are customarily administered by the i.v. route.
Chemical modification of the Vinca alkaloids has been rather limited. In the first place, the molecular structures involved are extremely complex, and chemical reactions which modify one specific functional group of the molecule without affecting other groups are difficult to develop. Secondly, dimeric alkaloids lacking desirable chemotherapeutic properties have been recovered or produced from Vinca rosea fractions or alkaloids, and a determination of their structures has led to the conclusion that these "inactive" compounds are closely related to the active alkaloids, frequently differing only as to stereochemistry at a single carbon. Thus, anti-neoplastic activity seems to be limited to very specific basic structures, and the chances of obtaining more active drugs by modification of these structures would seem to be correspondingly slight. Among the successful modifications of physiologically-active alkaloids has been the preparation of 6,7-dihydro VLB (U.S. Pat. No. 3,352,868) and the replacement of the acetyl group at C-4 (carbon no. 4 of the VLB ring system - see the numbered structure below) with higher alkanoyl group or with unrelated acyl groups. (See U.S. Pat. No. 3,392,173.) Several of these C-4 derivatives are capable of prolonging the life of mice inoculated with P1534 leukemia. One of the C-4 derivatives in which a chloroacetyl group replaces the C-4 acetyl group of VLB is also a useful intermediate for the preparation of structurally modified VLB compounds in which an N,N-dialkylglycyl group replaces the C-4 acetyl group of VLB (See U.S. Pat. No. 3,387,001). C-3 carboxamide and carboxhydrazide derivatives of VLB, vincristine, vincadioline etc. have also been prepared and found to be active anti-tumor agents. (Belgian Pat. No. 813,168.) These compounds are extremely interesting because, for example, the 3-carboxamides of VLB are more active against Ridgeway osteogenic sarcoma and Gardner lymphosarcoma than is VLB itself, the basic alkaloid from which they are derived. Certain of these amide derivatives actually approach the activity of vincristine against the same tumors. One of the amides, 4-desacetyl VLB C-3 carboxamide or vindesine, is currently being marketed for the treatment of malignancies, particularly in leukemias and related diseases. In humans, vindesine appears to have less neurotoxicity than does vincristine and is apparently effective against vincristine-resistant leukemias.
4-Desacetyl VLB C-3 carboxhydrazide is disclosed in Belgian Pat. No. 813,168 as being an active anti-tumor agent against transplanted tumors in mice. It has been shown to be active against Ridgeway osteogenic sarcoma, Gardner lymphosarcoma and P1534(J) leukemia. The search still continues for a more active alkaloid which has less side effects.